The invention relates to a method for the offset calibration of a magnetoresistive angle sensor for the determination of the directions of magnetic fields, which sensor comprises at least a Wheatstone bridge with at least four magnetoresistive resistors, which Wheatstone bridge is capable of receiving an input signal at its input side, in particular an input voltage, and which Wheatstone bridge is designed for supplying an angle signal at its output side, in particular an angle voltage, in dependence on the direction of a magnetic field which acts on the Wheatstone bridge, said Wheatstone bridge comprising a first and a second pair of mutually opposed, substantially parallel magnetoresistive resistors, the first and the second pair being arranged substantially at right angles to one another, while the direction of the magnetic field can be determined from the angle signal supplied by the Wheatstone bridge (by means of an evaluation circuit), and the invention also relates to a sensor device for measuring the angle of a magnetic field, comprising a magnetoresistive angle sensor which comprises at least a Wheatstone bridge with at least four magnetoresistive resistors, which Wheatstone bridge is capable of receiving an input signal at its input, in particular an input voltage, and which Wheatstone bridge is designed for supplying an angle signal at its output side in dependence on the direction of a magnetic field which acts on the Wheatstone bridge, said Wheatstone bridge comprising a first and a second pair of mutually opposed, substantially parallel magnetoresistive resistors, the first and the second pair being substantially orthogonal to one another, while the direction of the magnetic field can be determined from the angle signal supplied by the Wheatstone bridge by means of an evaluation circuit.
Such a method and such a sensor device are known, for example, from data book SC 17 "Semiconductor Sensors" of the Philips company. This known sensor device comprises a magnetoresistive angle sensor KMZ41 which consists of two Wheatstone bridges with four magnetoresistive resistors each. The two Wheatstone bridges are arranged so as to enclose an angle of 45.degree. with one another. An input voltage is applied to the input of each of the Wheatstone bridges. The output voltage of the first Wheatstone bridge is dependent on the angle of the magnetic field acting on the first Wheatstone bridge in a cosine function. The output voltage of the second Wheatstone bridge is dependent on the angle of the magnetic field acting on the second Wheatstone bridge in a sine function. The known sensor device is combined with an evaluation circuit which calculates the angle of the magnetic field from the output voltages of the first and the second Wheatstone bridges by means of the so-called Cordic algorithm. Irreproducibilities in the manufacturing process will in general render the magnetoresistive resistors of any Wheatstone bridge unequal, so that an unknown offset voltage will be added to each output voltage. An offset calibration is accordingly necessary so as to render possible an error-free angle measurement. The calibration in the known method takes place by means of a magnet which rotates in a very exact manner in front of the sensor. The offset voltages are determined iteratively through a comparison of the sensor output signal with a pulse width modulated signal. Such a calibration method is time-consuming owing to the iterative process, requires an expensive equipment on account of the rotating magnet during the calibration process, and requires additional inputs for the evaluation circuit, which are used for trimming only.